Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized for You

we will pick new questions that match your level based on your Timer History

Track Your Progress

every week, we’ll send you an estimated GMAT score based on your performance

Practice Pays

we will pick new questions that match your level based on your Timer History

Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.

It appears that you are browsing the GMAT Club forum unregistered!

Signing up is free, quick, and confidential.
Join other 500,000 members and get the full benefits of GMAT Club

Registration gives you:

Tests

Take 11 tests and quizzes from GMAT Club and leading GMAT prep companies such as Manhattan GMAT,
Knewton, and others. All are free for GMAT Club members.

Applicant Stats

View detailed applicant stats such as GPA, GMAT score, work experience, location, application
status, and more

Books/Downloads

Download thousands of study notes,
question collections, GMAT Club’s
Grammar and Math books.
All are free!

Thank you for using the timer!
We noticed you are actually not timing your practice. Click the START button first next time you use the timer.
There are many benefits to timing your practice, including:

Of the science books in a certain supply room, 50 are on [#permalink]

Show Tags

21 Apr 2012, 20:17

6

This post received KUDOS

16

This post was BOOKMARKED

00:00

A

B

C

D

E

Difficulty:

65% (hard)

Question Stats:

60% (02:29) correct
40% (01:59) wrong based on 356 sessions

HideShow timer Statistics

Of the science books in a certain supply room, 50 are on botany, 65 are on zoology, 90 are on physics. 50 are on geology, and 110 are on chemistry. If science books are removed randomly from the supply room, how many must be removed to ensure that 80 of the books removed are on the same science?

16. Of the science books in a certain supply room, 50 are on botany, 65 are on zoology, 90 are on physics, 50 are on geology, and 110 are on chemistry. If science books are removed randomly from the supply room, how many must be removed to ensure that 80 of the books removed are on the same science?

(A) 81 (B) 159 (C) 166 (D) 285 (E) 324

We can remove 80 books only from physics or from chemistry. Worst case scenario would be if we remove all books on botany, zoology, geology, 79 books on physics and 79 books on chemistry.

We would have 50(botany) + 65(zoology) + 50(geology) + 79(physics) + 79(chemistry) = 323 books and still won't have 80 books from the same science. As after this, only books on physics and chemistry will be left then any next book would become the 80th book either on physics or on chemistry.

Pretty much yes. For such kind of questions you should test worst case scenario to get the answer. Check the links in my previous post for similar questions.
_________________

Re: Of the science books in a certain supply room, 50 are on [#permalink]

Show Tags

04 Sep 2014, 16:29

Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.
_________________

Of the science books in a certain supply room, 50 are on botany, 65 are on zoology, 90 are on physics. 50 are on geology, and 110 are on chemistry. If science books are removed randomly from the supply room, how many must be removed to ensure that 80 of the books removed are on the same science?

Of the science books in a certain supply room, 50 are on [#permalink]

Show Tags

17 Dec 2015, 07:22

Bunuel wrote:

boomtangboy wrote:

16. Of the science books in a certain supply room, 50 are on botany, 65 are on zoology, 90 are on physics, 50 are on geology, and 110 are on chemistry. If science books are removed randomly from the supply room, how many must be removed to ensure that 80 of the books removed are on the same science?

(A) 81 (B) 159 (C) 166 (D) 285 (E) 324

We can remove 80 books only from physics or from chemistry. Worst case scenario would be if we remove all books on botany, zoology, geology, 79 books on physics and 79 books on chemistry.

We would have 50(botany) + 65(zoology) + 50(geology) + 79(physics) + 79(chemistry) = 323 books and still won't have 80 books from the same science. As after this, only books on physics and chemistry will be left then any next book would become the 80th book either on physics or on chemistry.

Of the science books in a certain supply room, 50 are on [#permalink]

Show Tags

03 Jan 2016, 11:44

What is the number at which picking one more book will guarantee that a thresold of 80 has been surpassed in one science?

Imagine you are playing a rigged game. The object of the game is for you to draw 80 books from the same science. The person attempting to cheat you out of winning picks out the books for you. He or she tries to prevent you from drawing the winning number of books until it is no longer possible to do so. He or she first starts off by picking books that cannot reach the 80 threshold and does so until such books are exhausted. He or she then starts picking books out of one the two remaining sciences until he reaches 79. To delay reaching the 80 thresold as much as possible he or she then shifts to the last science until he or she reaches 79. At this point it is no longer possible to cheat you out of winning and when the next book is drawn, you meet the 80 book threshold. The number of books drawn at that point is therefore 50 + 65 + 50 + 79 + 79 + 1 = 324.

Re: Of the science books in a certain supply room, 50 are on [#permalink]

Show Tags

09 May 2016, 15:02

I had a different approach.

You know that only books you can remove to get 80 of the same science is Physics (90) or Chemistry (110). Probability of drawing out a Chemistry is higher with every draw 110/365 vs 80/365. Logically you'll need to take out fewer books to 80 of the Chemistry. So you look at Physics books instead. Because the question says 'ensure'.

P(Physics) = 90/365 simplify to 90/360 or 1/4. You know that for every 4 books you take out 1 is likely to be a physics book. Then to get 80 physics books you need to take out 80 x 4 = 320. Answer is (E)

Re: Of the science books in a certain supply room, 50 are on [#permalink]

Show Tags

11 May 2016, 19:31

1

This post received KUDOS

[quote="Bunuel"]Bumping for review and further discussion*. Get a kudos point for an alternative solution!

Had an alternative approach

To ensure you get at least 80 books, you only look at Physics or Chemistry. 90 or 110. I calculated what percentage 80 books were of each group and took the highest percentage (i.e. 80/90 for Physics) and multiplied it by the total number of books (365). This makes sure you get 80 of one science as it makes sure you get 80 of the science that has the fewer books (i.e. harder probability). This gives you exactly 324.

gmatclubot

Re: Of the science books in a certain supply room, 50 are on
[#permalink]
11 May 2016, 19:31

Happy New Year everyone! Before I get started on this post, and well, restarted on this blog in general, I wanted to mention something. For the past several months...

It’s quickly approaching two years since I last wrote anything on this blog. A lot has happened since then. When I last posted, I had just gotten back from...

Happy 2017! Here is another update, 7 months later. With this pace I might add only one more post before the end of the GSB! However, I promised that...

The words of John O’Donohue ring in my head every time I reflect on the transformative, euphoric, life-changing, demanding, emotional, and great year that 2016 was! The fourth to...